1. Field of the Invention
The present invention relates to hydraulic apparatuses that are used to provide a resistive force and, more particularly, is directed towards hydraulic resistive apparatuses that are used in exercise equipment and cooling devices for dissipating heat generated by such apparatuses.
2. Description of the Prior Art
Exercise devices are often used to simulate aerobic exercises such as rowing, cross-country skiing, and stair climbing. The use of aerobic exercise devices is preferred as they can provide a continuous, steady work-out at a convenient location, for example, at home or an exercise facility. In order to more closely simulate a particular activity, these exercise devices are equipped with hydraulic and/or mechanical devices that provide a resistive force to arm and leg movement. A typical stair-stepping type exercise device employing a hydraulic device for providing the desired resistive force is marketed by CSA, Inc. under the trademark ALPINE CLIMBER.
The use of hydraulic systems for providing the resistive force utilized in exercising equipment is preferred since these systems have relatively few moving parts and are reliable. In general, a hydraulic system includes a cylinder and a piston that is reciprocally mounted in the cylinder. One of either the piston or the cylinder is mounted to a stationary member and the other one of the piston and cylinder is attached to a movable member. The desired hydraulic resistive force is produced by the restricted flow of a working fluid, for example, a hydraulic fluid, that is contained within the cylinder. Hydraulic resistive systems suffer from the disadvantage and limitation that as the hydraulic system is operated during a typical work-out it progressively becomes hotter and less resistive to compressive forces. The heat produced by the compression and restricted flow of the hydraulic fluid, and the friction between the cylinder and piston, causes a decrease in the viscosity of the hydraulic fluid within the cylinder. As the hydraulic fluid becomes less viscous, less force is necessary to move the piston and compress the hydraulic fluid. As less resistive force is provided by the hydraulic system the effectiveness of the exercise device decreases.
A need has arisen for a hydraulic resistive device that can be easily mounted on, and used in, exercise equipment and is capable of providing a substantially constant resistive force during an extended period of operation.